In Germany, the working-age population (those aged 15-64) is projected to decline by 15 percent between now and 2030, and the decline will be much steeper if immigration slows. Meanwhile, Germany's 65-plus population is set to grow by a third, to 27 percent from 20 percent. Its 80-plus population will grow by over half, to 8 percent from about 5 percent. Big increases in pension obligations, health-care costs and long-term care needs are thus in the offing.

In Japan, 30 percent of the population could be above age 65 by 2030, and nearly 13 percent--more than one in eight--could be 80 or older. Japan's working-age population, which has been falling since the mid-1990s, is projected to drop by another 16 percent between 2010 and 2030.

The U.S., meanwhile, can expect to see continuing population and manpower growth between now and 2030, thanks to relatively high birth rates and a robust inflow of immigrants (roughly half of them legal). America will remain the most youthful Western society, although its 65-plus population will be about 19 percent of the total, up from 13 percent today.